1. Field of the Invention
The present invention is directed generally to protection systems for battery packs.
2. Description of the Related Art
Battery packs generally have more than one battery cell internally housed in the battery pack such as generally depicted in FIG. 1 for a conventional battery pack 10 using an indefinite number, N, of lithium (Li) ion cells 12 electrically coupled between a first external terminal 14 and a second external terminal 16. As shown, the Li ion cells 12 are arranged in a series configuration, but in other battery packs the Li ion cells could be arranged in a parallel configuration or in a combination of a series configuration and a parallel configuration.
Battery cells, such as the Li ion cells 12 depicted are typically dependable, but on occasion an individual one of the Li ion cells may enter into a state causing such an undesirable internal condition as an overvoltage condition, which could potentially damage one or more other of the Li ion cells in the conventional battery pack or may potentially damage equipment (not shown) electrically coupled to the conventional battery pack 10. At other times, a charger or other external device (not shown) electrically coupled to the conventional battery pack may enter into a state that may result in an undesirable condition that may potentially damage one or more of the Li ion cells 12 of the conventional battery pack if the external device is allowed to remain electrically coupled to the conventional battery pack.
Conventional battery protection systems exist to help protect battery cells from undesirable internal and/or external conditions. For instance, a conventional protection system 18 is shown in FIG. 1 as having a conventional integrated circuit (IC) based battery protection circuit 20, and a conventional transistor pair 22 of a discharge transistor 24, and a charge transistor 26. The conventional protection circuit 20 includes an N cell Li ion battery conventional protection IC 28 and can also include one of more discrete devices 30 such as electrical resistors and/or capacitors and/or other discrete electrical components.
The conventional protection IC 28 is electrically coupled to circuit locations positioned between each of the series connected N number of the Li ion cells 12 for a total of N-1 number of electrical couplings from between a pair of the Li ion cells to the conventional protection IC. The conventional protection IC 28 also is electrically coupled to a circuit location positioned between the number 1 of the Li ion cells and the discharge transistor 24 of the conventional transistor pair 22 as depicted. The conventional protection IC 28 is electrically coupled to a circuit location positioned between the number N of the Li ion cells and the second external terminal 16. Consequently, the conventional protection IC is electrically coupled to either terminal of each of the Li ion cells 12 to allow, among other things, measurements of voltages conditions of each of the Li ion cells by the convention protection IC.
The conventional protection IC 28 is also coupled to the conventional transistor pair 22 of the discharge transistor 24 and the charge transistor 26, which allows, among other things, control of the open and closed circuit states of the conventional transistor pair acting as a switch dependent upon the presence or absence of a first state of the conventional protection IC.
In practice when an undesirable condition occurs, such as an overcharge condition in one of the Li ion cells 12, the conventional protection circuit 20 is in the first state to cause the conventional transistor pair 22 of the discharge transistor 24 and the charge transistor 26 to have an open circuit condition between the number 1 of the Li ion cells and the first external terminal 14 so that electrical current is no longer allowed to flow thereby protecting the Li ion cells and any external devices (not shown) electrically coupled to the conventional battery pack 10.
An implementation of the conventional battery pack 10 is shown in FIG. 2 as having three of the Li ion cells 12. The implementation has a version of the conventional protection system 18 with a version of the conventional protection circuit 20 that has a three-cell version of the conventional protection IC 28 and MOSFET versions of the conventional transistor pair 22 of the discharge transistor 24 and the charge transistor 26. Electrical resistors are used with the version of the conventional protection circuit 20 as the discrete devices 30 to couple the conventional protection IC 28 to circuit locations positioned between pairs of the Li-ion cells and a location between the number 1 of the Li ion cells 12 and the discharge transistor 24 of the conventional transistor pair 22.
Although the conventional protection system 18 gives a level of safety to the conventional battery pack 10, in certain circumstances, the conventional protection system can unfortunately, detract from the overall effectiveness of the conventional battery pack. In particular, if one of the components of the conventional protection system 18 inadvertently fails due to faulty conditions of the component rather than an undesirable internal or external condition described above, the conventional battery pack 10 will be rendered in this situation inoperable even though all of the internal Li ion cells 12 and externally coupled one or more external devices (not shown) are functioning properly. Consequently, the conventional battery pack 10 is disabled by the conventional protection system 18 even though no undesirable condition exists for which that the conventional protection system was designed to disable the conventional battery pack.